With the recent trend toward more compact and lower-profile electronic devices, the packing density of various types of electronic components, including a semiconductor device, a heat-generating device, and a Peltier device, is on the increase. As a circuit board on which such an electronic component is mounted, there is a heretofore known circuit board comprising a base body, metallic wiring layers disposed on both principal faces of the base body, respectively, and a through conductor for transmission of heat produced during operation of an electronic component from the metallic wiring layer disposed on one of the principal faces on which the electronic component is mounted to the metallic wiring layer disposed on the other principal face.
For example, Patent Literature 1 proposes a through electrode-equipped board constructed of a substrate formed of glass or ceramics and having a hole penetrating therethrough from the front side to the back side thereof in the direction of substrate thickness, the through hole being filled with a metal constituting an electrode. In this construction, the through hole has an opening diameter a of 80 μm to 500 μm; the ratio a/b (b represents the substrate thickness) falls in the range of 0.2 to 0.5; a metallic film C is formed in a thickness of greater than or equal to 0.2 μm on the surface of a part of the inner wall of the through hole which extends from each side of the substrate to a point at a distance of at least 50 μm below each side; and the through hole is filled with an electrode metal D which is lower in melting point than the metallic film C.